Addiction is characterized by a pattern of chronic and compulsive behaviour that causes significant impairment or distress in the individual. It is possible to become addicted both to substances, such as alcohol, street drugs, and prescription medications, as well as to self-destructive behaviours, such as gambling and sex. The maladaptive pattern of use that defines addiction results in tolerance to the substance or activity, so that more is needed to obtain the same effect. It also results in psychological and/or physiological dependence, and withdrawal symptoms can make it very difficult to control use or to stop using without professional support.